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<p>允许整数类型的值直接用于表达式。
</p>
<h3><span class="mw-headline" id=".E8.AF.AD.E6.B3.95">语法</span></h3>
<p>整数常量是拥有下列类型的<a href="value_category.html" title="c/language/value category">非左值</a>表达式
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">十进制常量</span> <span class="t-spar">整数后缀</span><span class="t-mark">(可选)</span>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">八进制常量</span> <span class="t-spar">整数后缀</span><span class="t-mark">(可选)</span>
</td>
<td> (2)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">十六进制常量</span> <span class="t-spar">整数后缀</span><span class="t-mark">(可选)</span>
</td>
<td> (3)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">二进制常量</span> <span class="t-spar">整数后缀</span><span class="t-mark">(可选)</span>
</td>
<td> (4)
</td>
<td> <span class="t-mark-rev t-since-c23">(C23 起)</span>
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>其中
</p>
<ul><li> <span class="t-spar">十进制常量</span> 是非零十进制数位（ <code>1</code> 、 <code>2</code> 、 <code>3</code> 、 <code>4</code> 、 <code>5</code> 、 <code>6</code> 、 <code>7</code> 、 <code>8</code> 、 <code>9</code> ），跟随零个或更多十进制数字（ <code>0</code> 、 <code>1</code> 、 <code>2</code> 、 <code>3</code> 、 <code>4</code> 、 <code>5</code> 、 <code>6</code> 、 <code>7</code> 、 <code>8</code> 、 <code>9</code>）
</li><li> <span class="t-spar">八进制常量</span> 是数字零（ <code>0</code> ）跟随零个或更多八进制数位（ <code>0</code> 、 <code>1</code> 、 <code>2</code> 、 <code>3</code> 、 <code>4</code> 、 <code>5</code> 、 <code>6</code> 、 <code>7</code> ）
</li><li> <span class="t-spar">十六进制常量</span> 是字符序列 <code>0x</code> 或字符序列 <code>0X</code> 跟随一个或更多十六进制数位（ <code>0</code> 、 <code>1</code> 、 <code>2</code> 、 <code>3</code>、 <code>4</code>、 <code>5</code> 、 <code>6</code> 、 <code>7</code> 、 <code>8</code> 、 <code>9</code> 、 <code>a</code> 、 <code>A</code> 、 <code>b</code> 、 <code>B</code> 、 <code>c</code> 、 <code>C</code> 、 <code>d</code> 、 <code>D</code>、 <code>e</code> 、 <code>E</code> 、 <code>f</code> 、 <code>F</code> ）
</li><li> <span class="t-spar">二进制常量</span> 是字符序列 <code>0b</code> 或字符序列 <code>0B</code> 跟随一个或更多二进制数位（ <code>0</code> 、 <code>1</code> ）
</li><li> <span class="t-spar">整数后缀</span> ，若提供则可包含下面一或两者，可以任何顺序出现：
</li></ul>
<dl><dd><ul><li> <span class="t-spar">无符号后缀</span> （字符 <code>u</code> 或字符 <code>U</code> ）
</li><li> <span class="t-spar">长后缀</span> （字符 <code>l</code> 或字符 <code>L</code> ）<span class="t-rev-inl t-since-c99"><span>或 <span class="t-spar">长长后缀</span> （字符序列 <code>ll</code> 或 <code>LL</code> ）</span> <span><span class="t-mark-rev t-since-c99">(C99 起)</span></span></span>
</li></ul>
</dd></dl>
 <table class="t-rev-begin">
<tr class="t-rev t-since-c23"><td>
<p>数位间可插入作为分隔符的可选的单引号（<code>'</code>）。编译器会忽略它们。
</p>
</td>
<td><span class="t-mark-rev t-since-c23">(C23 起)</span></td></tr>
</table>
<h3><span class="mw-headline" id=".E8.A7.A3.E9.87.8A">解释</span></h3>
<div class="t-li1"><span class="t-li">1)</span> 十进制整数常量（底 10 ，首位为最高位）。</div>
<div class="t-li1"><span class="t-li">2)</span> 八进制整数常量（底 8 ，首位为最高位）。</div>
<div class="t-li1"><span class="t-li">3)</span> 十六进制整数常量（底 16 ，首位为最高位，字母 'a' 到 'f' 表示十进制值 10 到 15 ）。</div>
<div class="t-li1"><span class="t-li">4)</span> 二进制整数常量（底 2 ，首位为最高位）。</div>
<p>下列对象被初始化为相同值：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">int</span> d <span class="sy1">=</span> <span class="nu0">42</span><span class="sy4">;</span>
<span class="kw4">int</span> o <span class="sy1">=</span> <span class="nu8">052</span><span class="sy4">;</span>
<span class="kw4">int</span> x <span class="sy1">=</span> <span class="nu12">0x2a</span><span class="sy4">;</span>
<span class="kw4">int</span> X <span class="sy1">=</span> <span class="nu12">0X2A</span><span class="sy4">;</span>
<span class="kw4">int</span> b <span class="sy1">=</span> <span class="nu6">0b101010</span><span class="sy4">;</span> <span class="co1">// C23</span></pre></div></div>
<p>下列对象也被初始化为相同值：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> l1 <span class="sy1">=</span> 18446744073709550592ull<span class="sy4">;</span> <span class="co1">// C99</span>
<span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> l2 <span class="sy1">=</span> <span class="nu0">18</span><span class="st0">'446'</span><span class="nu0">744</span><span class="st0">'073'</span><span class="nu0">709</span><span class="st0">'550'</span>592llu<span class="sy4">;</span> <span class="co1">// C23</span>
<span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> l3 <span class="sy1">=</span> <span class="nu0">1844</span><span class="st0">'6744'</span><span class="nu8">0737</span><span class="st0">'0955'</span>0592uLL<span class="sy4">;</span> <span class="co1">// C23</span>
<span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> l4 <span class="sy1">=</span> <span class="nu0">184467</span><span class="st0">'440737'</span><span class="nu0">0</span><span class="st0">'95505'</span>92LLU<span class="sy4">;</span> <span class="co1">// C23</span></pre></div></div>
<h3><span class="mw-headline" id=".E6.95.B4.E6.95.B0.E5.B8.B8.E9.87.8F.E7.9A.84.E7.B1.BB.E5.9E.8B">整数常量的类型</span></h3>
<p>整数常量类型是从依赖数字底和所用 <span class="t-spar">整数后缀</span> 的类型列表中，值所能吻合的首个类型。
</p>
<table class="wikitable">

<tr style="text-align:center">
<th colspan="3"> 允许的整数常量类型
</th></tr>
<tr style="text-align:center">
<td> 后缀
</td>
<td> 十进制底
</td>
<td> 其他底
</td></tr>
<tr style="text-align:left">
<td> 无后缀
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span> <span class="t-mark-rev t-until-c99">(C99 前)</span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span> <span class="t-mark-rev t-since-c99">(C99 起)</span>
</p>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(C99 起)</span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(C99 起)</span>
</p>
</td></tr>
<tr>
<td> <code>u</code> 或 <code>U</code>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(C99 起)</span>
</p>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(C99 起)</span>
</p>
</td></tr>
<tr>
<td> <code>l</code> 或 <code>L</code>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-until-c99">(C99 前)</span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(C99 起)</span>
</p>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(C99 起)</span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(C99 起)</span>
</p>
</td></tr>
<tr>
<td> <code>l</code>/<code>L</code> 与 <code>u</code>/<code>U</code>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(C99 起)</span>
</p>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(C99 起)</span>
</p>
</td></tr>
<tr>
<td> <code>ll</code> 或 <code>LL</code>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(C99 起)</span>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(C99 起)</span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(C99 起)</span>
</p>
</td></tr>
<tr>
<td> <code>ll</code>/<code>LL</code> 与 <code>u</code>/<code>U</code>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(C99 起)</span>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(C99 起)</span>
</td></tr></table>
<p>若整数常量过大从而无法符合后缀/底结合所允许的任何类型，且编译器支持扩展整数类型（譬如 <span class="t-c"><span class="mw-geshi c source-c">__int128</span></span> ），则常量可能以扩展整数类型给出；否则程序为谬构。
</p>
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
<p>整数常量中的字母无关大小写： <code>0xDeAdBaBeU</code> 和 <code>0XdeadBABEu</code> 表示同一个数<span class="t-rev-inl t-since-c99"><span>（一个例外是 <span class="t-spar">long-long-suffix</span> ，必须是 <code>ll</code> 或 <code>LL</code> ，不能是 <code>lL</code> 或 <code>Ll</code> ）</span> <span><span class="t-mark-rev t-since-c99">(C99 起)</span></span></span>。
</p><p>没有负整数常量。如 <span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">-</span><span class="nu0">1</span></span></span> 的表达式是将<a href="operator_arithmetic.html" title="c/language/operator arithmetic">一元负运算符</a>应用到常量所表示的值，可能会引起隐式<a href="conversion.html" title="c/language/conversion">类型转换</a>。
</p>
 <table class="t-rev-begin">
<tr class="t-rev t-since-c99"><td>
<p>当用于 <a href="../preprocessor/conditional.html" title="c/preprocessor/conditional"><tt>
#if</tt></a> 或 <a href="../preprocessor/conditional.html" title="c/preprocessor/conditional"><tt>
#elif</tt></a> 的控制表达式时，所有有符号整数常量都表现为如同拥有 <span class="t-lc"><a href="../types/integer.html" title="c/types/integer">intmax_t</a></span> 类型，且所有无符号整数常量都表现为如同有 <span class="t-lc"><a href="../types/integer.html" title="c/types/integer">uintmax_t</a></span> 类型。
</p>
</td>
<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td></tr>
</table>
<p>整数常量可用于<a href="constant_expression.html" title="c/language/constant expression">整数常量表达式</a>。
</p><p>由于<a href="translation_phases.html#.E6.9C.80.E5.A4.A7.E5.90.9E.E5.99.AC" title="c/language/translation phases">最大吞噬</a>规则，以 <code>e</code> 和 <code>E</code> 结束的十六进制整数常量在后随运算符 <code>+</code> 或 <code>-</code> 时，源码中必须以空白符或括号将它们与运算符分隔：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">int</span> x <span class="sy1">=</span> <span class="nu12">0xE</span><span class="sy2">+</span><span class="nu0">2</span><span class="sy4">;</span>   <span class="co1">// 错误</span>
<span class="kw4">int</span> y <span class="sy1">=</span> <span class="nu12">0xa</span><span class="sy2">+</span><span class="nu0">2</span><span class="sy4">;</span>   <span class="co1">// OK</span>
<span class="kw4">int</span> z <span class="sy1">=</span> <span class="nu12">0xE</span> <span class="sy2">+</span><span class="nu0">2</span><span class="sy4">;</span>  <span class="co1">// OK</span>
<span class="kw4">int</span> q <span class="sy1">=</span> <span class="br0">(</span><span class="nu12">0xE</span><span class="br0">)</span><span class="sy2">+</span><span class="nu0">2</span><span class="sy4">;</span> <span class="co1">// OK</span></pre></div></div>
<p>否则形成一个非法的预处理数字记号，这会进一步导致分析失败。
</p>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#include &lt;stdio.h&gt;</span>
<span class="co2">#include &lt;inttypes.h&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"123 = %d<span class="es1">\n</span>"</span>, <span class="nu0">123</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"0123 = %d<span class="es1">\n</span>"</span>, <span class="nu8">0123</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"0x123 = %d<span class="es1">\n</span>"</span>, <span class="nu12">0x123</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"12345678901234567890ull = %llu<span class="es1">\n</span>"</span>, 12345678901234567890ull<span class="br0">)</span><span class="sy4">;</span>
    <span class="co1">// 类型为 64 位类型（ unsigned long long 或可能的 unsigned long ）</span>
    <span class="co1">// 即使无 long 后缀</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"12345678901234567890u = %"</span><a href="../types/integer.html"><span class="kw207">PRIu64</span></a><span class="st0">"<span class="es1">\n</span>"</span>, 12345678901234567890u <span class="br0">)</span><span class="sy4">;</span>
 
<span class="co1">//  printf("%lld\n", -9223372036854775808); // 错误</span>
<span class="co1">// 值 9223372036854775808 不能适合 signed long long ，</span>
<span class="co1">// 它是无后缀十进制整数常量所允许的最大值</span>
 
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"%llu<span class="es1">\n</span>"</span>, <span class="sy2">-</span>9223372036854775808ull <span class="br0">)</span><span class="sy4">;</span>
    <span class="co1">// 应用到无符号值的一元减将它从 2^64 减去</span>
    <span class="co1">// 这给出无符号 9223372036854775808 </span>
 
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"%lld<span class="es1">\n</span>"</span>, <span class="sy2">-</span>9223372036854775807ull <span class="sy2">-</span> <span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="co1">// 组成有符号值 -9223372036854775808 的正确方式</span>
<span class="br0">}</span></pre></div></div>
<p>输出：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">123 = 123
0123 = 83
0x123 = 291
12345678901234567890ull = 12345678901234567890
12345678901234567890u = 12345678901234567890
9223372036854775808
-9223372036854775808</pre></div></div> 
</div>
<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
<div class="t-ref-std-17">
<ul><li> C17 标准（ISO/IEC 9899:2018）：
</li></ul>
<dl><dd><ul><li> 6.4.4.1 Integer constants (p: 45-46)
</li></ul>
</dd></dl>
</div>
<div class="t-ref-std-11">
<ul><li> C11 标准（ISO/IEC 9899:2011）：
</li></ul>
<dl><dd><ul><li> 6.4.4.1 Integer constants (p: 62-64)
</li></ul>
</dd></dl>
</div>
<div class="t-ref-std-c99">
<ul><li> C99 标准（ISO/IEC 9899:1999）：
</li></ul>
<dl><dd><ul><li> 6.4.4.1 Integer constants (p: 54-56)
</li></ul>
</dd></dl>
</div>
<div class="t-ref-std-c89">
<ul><li> C89/C90 标准（ISO/IEC 9899:1990）： 
</li></ul>
<dl><dd><ul><li> 3.1.3.2 Integer constants 
</li></ul>
</dd></dl>
</div>
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
<table class="t-dsc-begin">

</table>

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